Known methods of making an electrode for a battery or energy storage device use carbon as an active material and polytetrafluoroethylene (PTFE) resin as a binder. PTFE resin may fibrillate by applying shear to the resin. These fibrils hold carbon particles together, enabling carbon powder to be formed into a sheet. Fibrillation allows for PTFE to be used in lower loadings on a weight percent, and since it holds the carbon particles together by entanglement instead of coating, the large surface area of the activated carbon remains accessible to an electrolyte.
However, fibrillated PTFE binder particles will, unless lubricated, agglomerate with other fibrillated PTFE particles. If the fibrils agglomerate, the effectiveness of the PTFE as a binder is reduced. Liquid lubricants must be capable of wetting on the surface of the PTFE. Known of PTFE wetting agents include naptha, alcohols, MEK, and fluorosurfactants. Water does not wet PTFE, and therefore in a process that does not utilize organic solvents, lubrication must come from the carbon particles. This requires that the binder be very well dispersed in the carbon matrix prior to the application of shear.
Known methods of making carbon sheet for an electrode have the disadvantage of requiring organic solvents. These solvents, in addition to adding significant costs to the manufacturing process, create health, safety, and environmental issues.
Additionally, the solvents can be difficult to fully remove from the carbon sheet once the sheet has been formed. If solvent remains in the sheet, the sheet will not wet properly in aqueous electrolytes, resulting in poor electrochemical performance.